Process for toning silver pictures



Patented Mar. 7, 1933 UNITED STATES.

HANS MENGELE, or WIESBADEN, GERMANY, nssisnon v'ro 'BYK-GULDENWERKE GHEM'ISCHE FABRIK AKTIENGESELLSCHAFT, or BERLIN, GERMANY, A GORPOR-A-.

TION OF GERMANY PROCESS FOR TONING sILv RrIc'rUn s No Drawing. Application filed June 4, 1931, Serial l i'o. 542,108, and in Germany June 5, 1930."

ing baths have been used, which either contained gold or selenium as a tone giving substance. The material distinction of gold toning baths lies in the fact the former are much -more expensive than the latter and contain the tone giving ingredient as cation or as complexions. Principally on account of the lower cost the selenium toning baths have a steadily increasing demand. If, however, in spite of this gold toning baths are still in use, this is due tothe fact that selenium toning baths possess several disadvantages.

Mainly two groups of selenium toning baths must be distinguished, namely selenium toning baths, capable of toning all kinds of silver photographs including also such directly on a layer of silver bromide emulsions, i. e., without a preceding bleaching bath. These baths, however, afiect-owing to their strong acid or alkaline reaction-the hands of the worker and also the emulsion very disadvantageously. The other kind of selenium toning baths, however, does not possess this fault, but on the other hand it does not tone pictures on highly ripened halogen silver emulsions, particularly silverbromide emulsions and cannot produce the desired sepia tone without a preceding bleaching bath.

It has now been found that a sepia toning bath can be obtained, which on the one hand does not influence the hands of the worker and the emulsion, and on the other hand tones pictures on silver bromide emulsions in one single working process, i. e. Without a preceding bleaching bath. Such a bath which is the subject matter of thisinvention contains simultaneously a solution of selenious acid and one or more easily water soluble saltsof the sulphocyanic acid. It has been found that any and all salts of sulphocyanic acid, which dissolve in water relatively easily are very useful in connection with solutions of selenious acid.

A photograph inserted in such a solution shows within a few minutes a perfect sepia tone. Contrary to most of the toning baths,

a selenium toning both according to the pres GIItLlDVQDtlOH produces always the same-tone of picture on the same kind of emulsion;

.whereas toning baths heretofore known give exceedingly varying results in colour.

The addition of an organic acid to the solution greatly enhances the life of the toning bath, therefore increasing its efiiciency and also the number of pictures which can be handled by one and the same solution and bath without adversely influencing its other properties and qualifications. This feature is the more surprising, since the addition of organic acids to gold toning baths and the addition ofsalts of organic acids to other selenium toning baths has no stabilizing eflfect.

Another advantage of the tone bath according to the present invention is that it can be sold in powdered form, and when ready for use can be easily dissolved in a determined quantity of distilled water.

he following example 1 features of my invention:

s indicative of the Grams Ammonlum sulphocyanlde Citric acid 1 Selenious acid 0,5

are dissolved in 100 com. of distilled Water;

with this solution the photographs are then treated.

From the foregoing description of the preferred embodiment of the invention it will be noted that a composition is made which is highly eificient and easy to handle.

While one preferred embodiment of the invention has been disclosed it is evident that and a Weakly dissociated organic acid for increasing the efiiciency of said acid and salt.

3. A toning bath for photographic pictures comprising a solution containing ammonium sulphocyanide, a Weakly dissociated soluble organic acid, and selenious acid.

4. A toning bath for photographicpictures comprising an aqueous solution of ammonium-suiphocyanide, citric acid, and selenious acid.

5. A toning bath for photographic pictures comprising an aqueous solution of a sulphocyanide, citric acid, and se'lenious acid.

6. Acomposition for use in a'toningbath for photographic pictures comprising a Water soluble'salt of sulphocyanic acid, citric acid and-seienious acid.

Intestimony whereof I affix my'signature.

HANS lVEENGELE. 

